Hi again,
The #9 chord ,the bluesy one but which fits with so many differents moods,from blues to gipsy to rock to flamenco and jazz and so on...
A kind of super power chord.
The one you learn after playing since 6 month and people say :"waow I love this tone " and you don't know why but you do love it too.... And I still do not know why,
All the best.
Olivier
Edit : if you you extend the A13 to anEb#9 it becomes actually Ab13 flat fifth so be aware of the context,it might work ..or not..Sorry sorry.